1. Field of the Invention
The present invention relates to a piezoelectric vibrator and an acceleration sensor, particularly, relates to a piezoelectric vibrator used for oscillator, filter and sensor, and relates to an acceleration sensor using the piezoelectric vibrator.
2. Description of the Prior Art
As a piezoelectric vibrator using the piezoelectric effect, there is the piezoelectric vibrator which a piezoelectric element is formed on a surface of a vibrating body formed of constant elastic metal material and the like. As a vibrating mode of such piezoelectric vibrator, there are bending vibrating mode, thickness vibrating mode, twisting vibrating mode and longitudinal vibrating mode and the like. The piezoelectric vibrator is used for an oscillator, filter and sensor and the like.
In the conventional piezoelectric vibrator, it becomes difficult to support the piezoelectric vibrator due to the miniaturization. Vibration tends to leak through supporting portion of the piezoelectric vibrator, and the characteristics of the piezoelectric vibrator is deteriorated due to the vibration leakage. When some displacement or deformation occurs to the supporting portions of the piezoelectric vibrator by an external force, the characteristics of the piezoelectric vibrator varies largely.
FIG. 57 is an illustrative view showing an example of a conventional acceleration sensor. The acceleration sensor 1 includes a plate 2. One end of the plate 2 is fixed, and a weight 3 is attached to the other end of the plate 2. A piezoelectric elements 4 are formed on both surfaces of the plate 2. When an acceleration is applied in a direction perpendicular to the surface of the plate 2 of the acceleration sensor 1, the plate 2 bends as shown in FIG. 58. A voltage corresponding to the bending of plate 2 is generated in the piezoelectric elements 4. By measuring the voltage correspoonding to the bending of plate 2, the acceleration can be detected. The bending of the plate 2 can be increased by attaching the weight 3, and resulting in improvement of the sensitivity of the acceleration sensor 1.
When such an acceleration sensor is mounted on a car, the impact or the vibration due to unevenness of the road is often stronger than the acceleration of the car. Hence, such an acceleration sensor of cantilever-construction type is apt to cause misoperation or damage due to influence of impact attributable to unevenness of the road surface.
It is necessary to use a plurality of acceleration sensors in order to detect accelerations in a plurality of directions.